glacier glacial lake Glacial Processes and Landforms franzjoseph What is a glacier? • How do glaciers form? • What is a glacier? • A glacier is simply the existence of year-round ice on the landscape. • There are two broad types: continental and alpine. How do glaciers form? • Glaciers form whenever snowfall exceeds snowmelt year after year. The snow accumulates incrementally, pressure increases, and it is changed into névé and then ice by this pressure. FG19_01a Maximum Extent of Pleistocene Glaciation - 1/3 of land surface Most recent glacial maximum peaked 18,000 years ago and is considered to have ended 10,000 B.P. FG19_02 Current Extent of Glaciation - about 10% of land surface FG19_03 FG19_09 franz joseph landscape Franz Joseph Glacier and Outwash Plain, New Zealand Why is a glacier the only thing that is ever coming and going at the same time? FG19_10 Erosion by Glaciers • volume and speed determines amount of erosion. • erodes slightly more effectively than water. • plucking and abrasion (rock-tipped blade). • polishing and striations. • Continental glaciers remove all soil, plants, and small hills. • Alpine glaciers change V-shaped valleys to U-shaped. FG19_11a Yosemite%20Valley FG19_16 striations Striations Chipmunk jpg crevasses Transportation by Glaciers • will move material of all sizes, from glacial flour to massive boulders. • Slow transport. • Water in, on, and under glaciers (pluvial processes) moves much sediment as well. • FG19_12 till on glacier till on glacier dirty glacier Deposition by Glaciers • drift is any material deposited by glaciers or their meltwater. •Till is that unsorted material that is deposited directly by ice. • Moraines are linear features deposited at bottom or along sides of glaciers. • Glacial erratics are enormous boulders transported and deposited by glaciers, often far from their source region. FG19_14 medial moraine till Alpine Glaciers grinnell_lakes mikey on glacier FG19_23a FG19_23b FG19_27 FG19_27 bridal2b canada_mix_1 FG19_26 FG19_25 Moraines moraine FG19_35 FG19_37 glacier_Ellesmere_GSC Continental Glaciers or Ice Sheets • only two true ice sheets exist today: Greenland and Antarctica • where they meet the sea they can form ice sheets. • vary in thickness from hundreds of feet to two miles deep • scour away all soil and vegetation and dramatically reshape the landscape and ecology of large regions. • much change occurs in the periglacial environment. Ellesmere Island, Canada Continental Glaciers or Ice Sheets FG19_17a FG19_17b Continental Glaciers or Ice Sheets FG19_19 Finger_Lakes Finger Lakes Region, New York FG19_22 norway fjord Fjords ROGALAND Milford%20Sound